ACC - Automatic Climate Control

[jgohlke]

2009 Clubman S, manual tranny, sunroof, tinted windows, sunroof shade.

I do have ACC and don't find it very useful. The ACC just doesn't keep the car cool, so I've been using the AC on manual, mostly on MAX. Today I brought a digital thermometer with me and took some temperature readings. All temperature readings are in F.

Morning, 6:00am, still dark, 77 degrees. I put the temperature probe into one of the vents, started the car and drove off. Within a couple of miles, the temperature was reading 46. Clearly the AC can blow plenty cold.

I played around with HVAC controls on the way to work. Keeping them on manual (regular or max), the temp at the vent stayed at 46. On ACC (set at 74), the vent temp was 56. On this setting, even in the dark, the cabin was a little warm for me. I didn't take a cabin temp reading.

After work (car sat outside all day, it was sunny and hot, outside air temp in the low 90s), the car was 114 inside when I got in. I ran the AC on MAX for several miles and the car cooled right down. I fiddled with the AC controls until the car was comfortable and then drove for a while to let the temperature stabilize. The cabin temperature (front, passenger seat) was 75. Then I turned the ACC on and set the desired temperature. At each temperature change, I monitored the digital thermometer until it stabilized.

ACC -- CABIN
74 -- 86
72 -- 82
70 -- 79
68 -- 75

The good news is the AC seems to work ok and the ACC behaves appropriately (running the fan on high at first, then stepping the fan down as the cabin cools off). The ACC just steps down too quickly. I think it is just very badly calibrated.

Does anybody know if this can be adjusted/re-calibrated by the dealer? Is is possible to relocate the temperature sensor? Does anybody know where the temperature sensor is located?

Appreciate the help!

[gawannamini]

Yea, I find myself fiddling with the temp setpoint constantly. I have a convertible and run it on MAX when the top is down. What I have found is that the fan is a bit on the weak side and when in auto control it will slow the fan down so much that you can barely feel the cold air. It just does not project very well. The large vent on top of the dash robs a fair amount of air from the dash vents.

I think you are on the right track. It seems like the temp sensor is too close to the outlets and does not reflect cabin temps very well.

[RJKimbell]

We have no issues at all with our ACC, it works great, we vary the Temp. to meet the conditions we want. Today it was a Defrost Day, the outside temp was 65 and rainy, even the Sunroof fogged up. I ran the fan speed on High and 72, it cleared the windows and kept us comfortable until we got home. If I get chilly when we run the AC, I just close the vents so Hubby gets the blast!!

[jgohlke]

Originally Posted by RJKimbell

We have no issues at all with our ACC, it works great, we vary the Temp. to meet the conditions we want. Today it was a Defrost Day, the outside temp was 65 and rainy, even the Sunroof fogged up. I ran the fan speed on High and 72, it cleared the windows and kept us comfortable until we got home. If I get chilly when we run the AC, I just close the vents so Hubby gets the blast!!

Since you live up north and I live down south, we'll have very different experiences with the climate controls. It's nice to know I can expect the heat to work pretty well (when winter eventually shows up....)

Like you, I can run the ACC on 64 or 66 and keep the car comfortable. Comfort isn't the issue. The issue is the car isn't 66, it's more like 76.

If I ignore the actual temperature readings on the ACC and just use it as a hot-to-cold dial, it works fine. Does it really matter if I set it to 64 to keep the car 76? No. The engineer in me finds great fault with that approach, though. If the HVAC controls have a temperature setting, it should have some basis in reality for the actual temperature of the car.

Since the car is so computer controlled, I was hoping the temperature setting could just be re-calibrated (make the car think it is 10 degrees hotter than the temperature probe reports). Or maybe just move the temperature probe from where it is (too close to the vent, I suspect) to somewhere in the cabin where it's warmer (and where I am).

[someguyfromMaryland]

Igohike,

I never would have guessed you were an engineer. 8)
Instead of engineering a modification to a sophisticated design, why don't you just apply an internal conversion factor (say, -10 degrees) to the temp selector?
I think the real problem is your not measuring the temp in the same place the ACCis measuring, which is usually up near the rear view mirror.
HTH!

[RJKimbell]

I understand your frustations, maybe it's time for a Dealer visit. We do have HOT Temps., though many don't think it gets to 108 here, but it did this Summer very High Humidity, still the ACC worked as expected.

[corcoranwtnet]

Whatever you do, DON'T manually calculate your gas mileage! You'll find that the MPG reading on your dash is way off...same as your speed in MPH measured vs. a GPS unit.

MINI/BMW seems to think that "happy" numbers are more meaningful than actual numbers. Just use the readings as indicators of "higher" or "lower", not actual readings. (You'd have to pay a lot more for actual readings, no doubt).

[russgriz]

I would think that the temp sensor for the automatic AC would be somewhere near where the cabin air first enters the HVAC system. That would be the closest representation of cabin temp. Anyone have any thoughts on this?

[Oxybluecoop]

The temp sensor for the auto recirc is behind the battery under the passenger front cowel. The solar temp sensor is the little bump in the center of our dash behind the defrost vent and the evaporator temp sensor is in the panel to the right of the gas pedal.

[jgohlke]

Originally Posted by corcoranwtnet

Whatever you do, DON'T manually calculate your gas mileage! You'll find that the MPG reading on your dash is way off...same as your speed in MPH measured vs. a GPS unit.

MINI/BMW seems to think that "happy" numbers are more meaningful than actual numbers. Just use the readings as indicators of "higher" or "lower", not actual readings. (You'd have to pay a lot more for actual readings, no doubt).

Ha, ha....Too late! I use Gas Cubby on my iPhone to keep track of all that stuff and of course I have a GPS! I didn't trust the car numbers from day 1. For what it's worth, my son drives a 2009 Acura TSX and also uses Gas Cubby. He finds the same results. Acura overestimates the car's MPG as well.

[jgohlke]

Originally Posted by RJKimbell

I understand your frustations, maybe it's time for a Dealer visit. We do have HOT Temps., though many don't think it gets to 108 here, but it did this Summer very High Humidity, still the ACC worked as expected.

108! That's hot!

You say the ACC works "as expected". Can you elaborate?

When it was hot there, did you have to set the ACC lower than the real temperature to keep the car cool?

I'm curious to know if the ACC keeps the car at the temperature you set or if you are just adjusting the temp as necessary for comfort.

After a few days of experimenting, I find that I can set the ACC on 68 and the ACC system keeps the car cabin comfortable. The cabin temp (at the front seats) is 75-76.

[gawannamini]

I'm in Atlanta and mine does the same as jgohlke. I set it down the in the mid 60's to keep the cabin at low 70's. Also if I set it at 72 the fan speed is so low you can hardly feel it.

[MotorMouth]

Originally Posted by corcoranwtnet

Whatever you do, DON'T manually calculate your gas mileage! You'll find that the MPG reading on your dash is way off...

I reset my OBC and calc by hand each tank. very rarely is the onboard off by more than 1 mpg.

[RJKimbell]

Originally Posted by jgohlke

108! That's hot!

You say the ACC works "as expected". Can you elaborate?

When it was hot there, did you have to set the ACC lower than the real temperature to keep the car cool?

I'm curious to know if the ACC keeps the car at the temperature you set or if you are just adjusting the temp as necessary for comfort.

After a few days of experimenting, I find that I can set the ACC on 68 and the ACC system keeps the car cabin comfortable. The cabin temp (at the front seats) is 75-76.

Yes JG that was HOT!! And I'm a Sun Bum grew up in AZ so I know what HOT is!!

Elaborating...(if you need more clarification later...just ask)
We use Auto almost exlcusively. Hubby has a problem with bieng hot, so temps. are usually set at LOW starting out...this gets the car pretty Cold except on those extremely Hot Days then it takes a min. or two.

On not so Hot Days it is set around 66-68, outside Temps. in the Low 80's. Once the ACC is set at a constant Temp. we usually don't touch it. I couldn't tell you exactly what the Interior Temp. is, but it's Auto-AC so it is supposed to be what you set it at isn't it??

I sometimes hear a variation in speed, but don't feel anything like gain or loss of power, I'm guessing this would be either the Fan or Compressor.

I was down in AZ in March of this year and though it is not their hottest part of the year, on my 3,000+ mile round trip journey, Molly kept me quite comfortable. Sunroof OPEN when ever possible, but I had the ACC on too!!

Hope you find the answers you are looking for...I still think a Dealer trip is in order.

[jgohlke]

Originally Posted by RJKimbell

On not so Hot Days it is set around 66-68, outside Temps. in the Low 80's. Once the ACC is set at a constant Temp. we usually don't touch it. I couldn't tell you exactly what the Interior Temp. is, but it's Auto-AC so it is supposed to be what you set it at isn't it??

Thanks for the update. Based on this paragraph of your response, I think you are having the same "problem" as I am...unless you are a polar bear and your car is really 66 inside. :-)

In fact, it IS supposed to be the temp you set it....that's kinda the problem...it's not. We went about solving the problem in different ways. You guys just turned your ACC temperature setting down until the car was comfortable and didn't get too hung up on the actual temperature display.

I flipped mine over to max and used the fan speed to regulate the cabin temperature. It isn't a big deal and we are both keeping our car's cabin comfortable.

It's only an issue for me because I've never had a car with ACC before and the salesperson (who was great, btw) talked me into it. Of all the features the new car has that the old one didn't, this is the one I was most excited about. it's just kind of disappointing to find out it doesn't work like I expected and consequently, I'm not using it.

As an experiment, I've been driving around for the last couple of days using the ACC exclusively. Mostly it stays set at 68 with an occasional bump to 66 if I get too warm. It seems to work ok and does in fact, keep the cabin a comfortable temperature (76). As a side note, my son and I did some errands together yesterday and he drives a 2009 Acura TSX. He said his car does the same thing when he uses the ACC....starts off blowing cold, but steps down too quickly and the cabin gets too warm for the setting. He alternates between adjusting the temp (lower) and kicking the fan up a notch.

Place like Florida (and WA! Who knew....) that get reasonably high temps and very high humidity, coupled with strong sunlight are probably at the extreme end of the design envelope for car makers. Add to that mix a small engine and the desire to get high MPG numbers, it makes it attractive to the car makers (and their salespeople) to have the ACC system shifted to the "warm" end of the spectrum. (making heat for the car is almost free in terms of MPG)

The marketing folks then get to say, "Hey, set your car to 76 and just forget it and you'll still get 35 MPG". What they don't say is that it will be 90 inside the cabin.....because if the car was really 76 inside, the AC would be cycling on a lot more and you would only be getting 29MPG (like I am).

It isn't a big deal and only surprising because the car is so well (over?) engineered in other areas, it is surprising that the ACC is so out of spec. If the thermostat in my house was so far off, I would call somebody to come fix it!

[jgohlke]

Originally Posted by MotorMouth

I reset my OBC and calc by hand each tank. very rarely is the onboard off by more than 1 mpg.

My calculations show a similar difference.

Gas Cubby 29.7 MPG

The car 30.9 MPG

Both the car and GC know the exact mileage (I enter it into GC). The car is measuring the gas consumed, but I don't know exactly how. For GC, I enter the gas (measured at the pump). Between the two gasoline measuring systems (the car and gas pump), I'm believing the gas pump to be more accurate.

[RJKimbell]

Fuel Economy is something that I'd like to change. I just filled up last night, drover 250.3miles, put in 9.909gal. Averaged 24.3mph (key) and got 27.645mpg. This is typical, our commute is 40+ miles a day, plus we use Molly for our Weekend Errands. It certainly beats our 12mpg '01 Dodge Durango though!!

[jgohlke]

Originally Posted by RJKimbell

Fuel Economy is something that I'd like to change. I just filled up last night, drover 250.3miles, put in 9.909gal. Averaged 24.3mph (key) and got 27.645mpg. This is typical, our commute is 40+ miles a day, plus we use Molly for our Weekend Errands. It certainly beats our 12mpg '01 Dodge Durango though!!

Almost 28 MPG isn't bad. Unfortunately, your car, like mine and many others is a little optimistic about reporting the MPG numbers....You are really getting 25 MPG. (250.3 / 9.909 = 25.26).

[MotorMouth]

Originally Posted by jgohlke

My calculations show a similar difference.

Gas Cubby 29.7 MPG

The car 30.9 MPG

Both the car and GC know the exact mileage (I enter it into GC). The car is measuring the gas consumed, but I don't know exactly how. For GC, I enter the gas (measured at the pump). Between the two gasoline measuring systems (the car and gas pump), I'm believing the gas pump to be more accurate.

True the gas pump measuring system is always more accurate unless the pump isn't calibrated (starting a conspiracy theory here haha).

Just saying my OBC and yours too it seems, is pretty accurate.

[corcoranwtnet]

I've had my (unmodified) MCS for a year now and have calculated all but one or two tanksful manually. My OBC has never read less than 3 mpg above the calculated mileage. It usually reads 25-26 mpg for local tanks (2-3 mile trips with stoplights and stop signs) and I calculate 22-23 mpg.

The best mileage I've ever gotten (constant 70 mph with a/c for a full tank) was calculated to be 34.4mpg. The OBC said I got 40.

Therefor I assume +/-10% error on the OBC...but I still think the gas mileage is great.

[Wilade]

Jgokle, what color is your headliner?

I had always supected my anthracite (black) color headliner was radiating heat into the cabin. I confirmed my suspicions earlier this year when my car was being serviced. The loaner car the dealer gave me had a cream colored headliner. I could tell a big difference between the two. I had to actually turn the temperature up to be comfortable.

[NightFlyR]

No Problems with my ACC this past summer, biggest problem i have is when it rains I have to keep the defrost on or everything just fogs up.

[Kenbob]

Unfortunately most gauges on cars these days are set for marketing reasons (to make the driver feel good) rather than information. One exception was my Boxster which was very accurate on the speedo and fuel gauge. It's actually a little disconcerting at first to see the fuel gauge start dropping from full almost immediately unlike most vehicles that use 2/3 of a tank by the time they show 1/2.

My MCS will show full for almost 100 miles. It is also optimistic by a couple MPG's on the computer, the speedo reads 73 at a GPS indicated 70, and I always leave my ACC set at 68. I'm sure it's closer to 75 in the cabin. As an engineer also, I would prefer accurate info delivered to me, but the majority of drivers will never verify the numbers so it's more important to make them feel good.

[jgohlke]

Originally Posted by Wilade

Jgokle, what color is your headliner?

I had always supected my anthracite (black) color headliner was radiating heat into the cabin. I confirmed my suspicions earlier this year when my car was being serviced. The loaner car the dealer gave me had a cream colored headliner. I could tell a big difference between the two. I had to actually turn the temperature up to be comfortable.

Headliner is gray. With the giant sunroof, there really isn't very much headliner, so I don't think it's an issue. I did put my hand on it and felt around today while I was driving on a sunny day. It felt cool like the rest of the interior.